Introduction: How to Clean a Small Fish Tank and Filter Using a Siphon

About: Inventor and Emergency Doctor.

I have owned my goldfish tank for many years now and love the gentle, relaxed ambience it brings to our kitchen. In this Instructable I will explain how to clean a small fish tank and filter using a siphon. It is not difficult and takes about 15 minutes once a week but there are a few important things you need to know.

It is important to change part of the water regularly otherwise the fish may become stressed and unwell or could die. Regular testing with a multi-test dipstick will tell you whether the water quality is good. If there is a problem you may need to do more frequent small changes. Problems can develop quickly, particularly if you are not experienced with fish tanks or if you tank is well stocked. Dipsticks will give you the information you need.

Waste builds up in the tank; some of it you can see, some of it you can't. Nitrates and phosphates are not visible with the naked eye, unlike the debris that builds up in the bottom of the tank. By siphoning some of the water away, you will take both visible and invisible waste away with the water.

Always wash your hands before and after cleaning out your tank. Make sure you rinse them thoroughly, even small amounts of detergents and cleaning products can harm aquatic creatures.


I have provided links to useful products on Amazon for your reference.

Multi-test dipsticks

Washing up bowl/large pan/bucket

Large jug, I use a 2L variety

Bottle brush or tooth brush These baby bottle brushes are good because they go round the corner.

Clean tea towel

Fish tank siphon This one is for a large tank, there are others with a bulb you squeeze to get the water flowing.

Tap water conditioner. This is the one I use;

Step 1: Using the Brush to Remove Algae

Use a clean, dedicated bottle brush to remove algae by gently scrubbing the walls of the tank and any ornaments which are affected. In the past when I have had a few snails I have needed to do this very little, if at all.

Step 2: Using the Fish Tank Siphon

The siphon is simply an extendable tube which pumps some of the water out and allows you to remove waste at the same time. To fill the siphon immerse the whole of of the rigid wide tube in the fish tank along with most of flexible tube. Move it around until it is full of water then pinch the end to stop the water flowing back into the tank, pulling it into the washing up bowl. You need the water level in to tube to be below the level in the tank for the water to flow. When you let go of the pinch the tube will act like a siphon and will start to drain water from the tank for you. Make sure the end of the tube stays in the bowl otherwise you will get wet feet!

The amount of water you remove may vary depending on how how stocked your tank is. 10 to 15% is usually recommended but I find that I need to change around 20% in order to keep the nitrogen levels low. Start with 10%, test the water weekly and you will get a feel for how much water you need to change. You mustn't remove more than you need to as this can destabilize the tank and upset the inhabitants. Friendly bacteria build-up in the water, in the stones and on the filter and removing large amounts of water can affect the balance. Using the siphon like a vacuum cleaner, gently go over the gravel at the bottom of the tank and turn it over so that it sucks up loose debris. If gravel sticks in the end of the tube you can pinch or bend the flexible end to reduce the suction and gently tap it against the side so that the stones fall out.

Even if the water looks clear it can be surprising how much debris can build up in the bottom of the tank. This is from uneaten food and faeces as well as algae and plant debris. It is best not to top up the water if the level drops as this does not remove any waste. When the level drops from evaporation this concentrates waste rather than removing it, topping the water up up is not a good idea without removing some of the water first.

You don't need to remove your fish from the tank for a normal clean, just be gentle and quiet so as not to upset them.

Step 3: Cleaning the Fish Tank Filter

It is better to clean the filter on a different day to that on which you vacuum the stones as it can upset the bacterial balance of the tank. Slide the filter up the wall of the tank or lift it clear of the water when you remove the sponge otherwise if it is heavily clogged large amounts of debris can be shed into the tank. Hold the sponge under the flowing water from the siphon and gently squeeze it a few times to get most of the debris out.

DON'T run it under the tap. DON'T clean it with soap. The aim of cleaning it is to remove loose debris. One of the important uses of the filter is as a home for friendly bacteria. You don't want to remove these bacteria by cleaning it too aggressively.

Step 4: Replacing the Water

DON'T put plain tap water in your fish tank; it will kill your fish. This was why my pet goldfish only lasted a few weeks in the 1980s; my mum used to keep them in a bowl of tap water, as everyone seemed to then. Use a tap water conditioner such as Tapsafe, Aquasafe or similar. This contains a chelating agent which binds chlorine and makes it settle out of the water, making it safe for the inhabitants of your aquarium. Follow the instructions; it's usually a few millilitres per litre. I put at least 5mls in every 2 litre jug; the instructions said it should have been about 2.5mls but I was finding the chloride level was creeping up. All the research I have done shows that adding too much tap water conditioner is harmless.

Please add any tips in the comments below.

The Amazon links I have used here are Affiliate links. This means I get a few pence if you buy something! Please help support my Instructables by using the links to buy anything you need, it won't cost you any extra. Thank you!